Hardening of gelatin



United States Patent HARDENING 0F GELATIN George July, Edward BowesKnott, and Felix Pollak, Wealdstone, Harrow, England, assignors toEastman Kodak Company, Rochester, N. Y., a corporation of New Jersey 15N0 Drawing. Application December 3, 1952,

Serial No. 323,924

7 Claims. (Cl. 117-62) This invention relates to the hardening ofgelatin particularly in photographic emulsions with1:3-dihydroxymethylbenzimidazol-Z-ones.

In the case of gelatin which is to be treated with aqueous solutions, asexemplified by photographic emulsions which are treated with'processingsolutions, it is particularly desirable that the gelatin have propertieswhereby it is resistant to the effects of the aqueous solution. It is aparticular advantage if the gelatin material is not only resistant towater at normal temperature but to water at elevated temperaturesbecause in the case of photographic emulsions resistance to hot waterwould permit the hot processing of the gelatin emulsion thus shorteningthe time for the processing operations.

One object of our invention is to provide a gelatin which is resistantto the effect of water at elevated temperature. Another object of ourinvention is to provide gelatin photographic emulsions which may be hotprocessed without break down of the physical structure thereof. Afurther object of our invention is to provide compositions of gelatin inwhich a small amount of a 1:3- dihydroxymethylbenzimidazol-Z-one ispresent therein. Other objects of our invention will appear herein.

We have found that when gelatin is treated with a 1:3-dihydroxymethylbenzimidazol-Z-one, or any gelatin layers or photographicgelatin emulsion layers are treated with a1:3-dihydroxymethylbenzimidazol-2-one, the resulting product isresistant to the effect of hot water or of hot aqueous processingsolutions and that in the case of photographic emulsions so treatedhigher speed and gamma are obtained than with emulsions not so treatedand having equal fog characteristics or where equal development timesare used higher speed and gamma and lower fog characteristics areobtained than for emulsions not so treated. We have found that gelatinhardened in accordance with our invention is useful either in colorphotography or in black-and-white photography.

The hardeners which are-employed in accordance with our invention havethe structural formula:

(IJH2OH Where R is either hydrogen, alkylor a halogen substituent.Qompoundsof this type may be prepared as illustrated by the followingexamples.

Example 1 benzimidazol-Z'fo'ne was obtained melting at 163-464 C.

$332,316 C6 Patented Jan. 24, 1956 Example 2 i 2 parts of5-methylbenzimidazol-2-one was mixed with 10 parts of water and 5 partsof 40% formalin and the mixture was slowly warmed so as to dissolve thesolid material therein. The solution thus formed was filtered and cooledto 0 C. which resulted in the formation of pale orange, sandy crystals.These crystals were separated from the liquid and recrystallized fromhot water. 2 parts of 1:3-di(hydroxymethyl)-5-methyl-benzimidazol- 2-onemelting at 176-178 C. was obtained.

In the carrying out of our invention the gelatin may be hardened eitherby incorporating hardener directly in the gelatin, or layers of gelatinwhich have been coated out onto a support may be treated with a solutionof the hardener so as to impart a hardening eflect thereto. Thehardening action on the gelatin in accordance with our invention takesplace to the best effect at a pH value of at least 8. Although thehardener in accordance with our invention modifies the properties of thegelatin when employed therewith in any proportion, we have found thatamounts of the hardener within the range of .1-10% based on the weightof the gelatin are the most desirable in carrying out the hardening ofgelatin in accordance with our invention. In the compounds'employed forhardening in accordance with our invention the benzene ring therein mayeither be unsubstituted except for the imidazole ring thereon or analkyl or halogen substituent may be present on the benzene ring. If analkyl group is the substituent on the ring it is desirable that it beselected from those alkyls which have 1-4 carbon atoms such as methyl,ethyl, isopropyl or the like. If a halogen substituent is employed thissubstituent is most desirably chlorine although the hardening action onthe gelatin treated therewith will be efiective if some other halogensubstituent such as bromine or fluorine is used.

The following examples illustrate the hardening of gelatin in accordancewith our invention:

Example 3 A strip of photographic film having three layers of a gelatinemulsion thereon each sensitive to a different color such as is employedin color photography was immersed for 4 minutes at F. in a solutionconsisting of 1 gram of 1:3-dihydroxymethylbenzimidazol-Z-one, 15 gramsof sodium sulfate, 100 cc. of Water and a sodium borate-boric acidbuffer to maintain the solution at a pH of 9. After immersing the filmstrip for the specified time it was rinsed in water at 100 F. for twominutes and thendeveloped at 100 F. The film strip was subjected towashing with water having a temperature of F..and no change occurred inthe emulsion layer. 1

' Example 4 v The procedure of Example 3 .was repeated except that thehardening solution was maintained at a pH of 8 and the film was driedfirst and then subjected to photographic processing. The resulting filmstrip was subjected to a washing with Water having a temperature of 160F. and no change was. found to occur in the emulsion layer.

Example 5 The procedure of Example 4 was repeated but with the additionthat after drying the film it was immersed in a solution in Water ofresorcinol 04%) and resorcylic aldehyde A very hard film was obtained.In proceeding according to the above examples it was found that when thelayers were processed according to Examples 4' and 5 that the resultingemulsion layers had similar photographic properties and a highphotographic density was obtained thereby.' It was also noted in theseexamples that the'speed of the yellow layer was not as great as in thecase of those emulsions which had not been subjected to such hardening.However, this lowering of speed could readily be compensated for byincreasing the first development time. In many cases the speed reductionofthe yellow layer is of advantagc such as in those color processeswhich sufrer from a too rapid deyelopment of the yellow layer. Thehardening of the emulsion layer as describedin Example 3 gave goodresults and was fully equivalent to that obtained with formalinhardening but with the additional advantage, however, t a n t e e pit om n er q wa in wa r ft t tm n t he f m n n q uq s' e .h e fog in the yewla s he a inthe sa s 19 th ,.,fi m strip harde i sq id qen i h ,Qiavent q n s oa ingre l s T ellq na s sime re them uetharde ned inaccordance with our invention and that hardened with formalin.

Control Test Solution (formalin) Hardening time 1 min. 4 min. sec. 40sec.

Development time 4 4 4 4 F 0.21 0.21 0. 0.27 2.35 2:20 :2. 18 2. 09 1.03 0. 95 0. 80 0. 74 8 8 8 8 0. 31 0. 42 0.50 0. 66 2. 35 2. 26 2. 16 1.96 1. 64 L26 1.17 1.00

s it the ef fn h rf a m nt times the emulsion hardened in accordancewith our invention exhibited higher speed and gamma andlower fog than inthe case of the forrnalin hardened emulsion. V I c I We have also foundthat the hardeners referred to above are efiective for hardening gelatinwhen incorporated in compositions thereof as illustrated by thefollowing examples:

Exainple 6 Three samples of a gelatin-silver halide negative emulsionwere taken and in two of those samples hardeners in accordance with ourinvention were incorporated. The melting point of the emulsion wasincreased by those additions as shown by the following:

901 melting point of untreated emulsion.

146 melting point of the emulsion to which has been added 4 gram ofl:3-di(hydroxymethyl)-beniimida- ZoI-Z-one perliter of emulsion. I c H207 F. melting point of emulsion containing 1 gram of 1;3-di(hydroxymethyl)-benzirnidazol-2-one per liter of emulsion.

Upon coating out of the emulsionandsubjec ting thesame to incubation thehardening thereof is still further increased.

ramble"? fast negative chlorobromide gelatin emiilsion was taken and onesam ple was untreated and two samples Example 8 16 mm. film havingthereon a highly sensitive emulsion was immersed in a solution for twominutes having the following composition:

0.3 part of 1:3-di(hydroiiymethyl)-5-methylbenzimidazol-2-one 15 partsof NazSO4 2 parts of NaaCOaHaQ W Water to make parts.

The film after hardening in this solution at lOOf F. for two minutes waswashed with water for one minute and then processed in ahydroquinonem'etol type developer for 4, 8 and 16 minutes. The filmafter processing was examined and was found to bew'e'll hardened foreach of the various development times which were used. This hardeningcompound was also employed to treat photographic film of the color typehaving three layers of differcnt color sensitivities thereon. It wasfound that the resulting product had excellent hardness and fog was keptto a minimum.

We claim:

1. A composition of gelatin and a compound having the structural formulacrnon -N (2117011 R being a substituent selected from the groupconsisting of hydrogen, lower alkyl chlorine, bromine and fluorine.

2. A composition of gelatin and l'z3-dihydroxymethylbenzimidazol-2-one.

3. A composition of gelatin and 1:3-dihydroxymethyl- S-rne'thylbenzimidazol-Z-one.

4. A method of hardening a gelatin layer which comprises immersing thelayer in an aqueous solution of a compound having the structural formula(IZHaOH -N (ijHaOH R being a substitiient selected from the groupconsisting of hydrogen, lower alk'yl chlorine, bromine and fluorine. 5.method of hardening a gelatin layer which comprises immersing the layerin an aqueous solution of 1:3- dihydroxymethyI benZimidaZoI-Z one.

6. Arnethod of hardening a gelatin layer which coinprises incorporatingin an aqueous gelatin composition 21 small'proporti0n of a compoundhaving the structural formula:

prises incorporating in "anfaque'ous gelatin composition a smallproportion of l:3 dihydroirymethyl benzirnidazol- 2-one and coatingout'the resulting composition onto 11 support therefor.

hars ness Cited'inthe file of t h ispate'nt UNITED STATES PATENTS

4. A METHOD OF HARDENING A GELATIN LAYER WHICH COMPRISES IMMERSING THELAYER IN AN AQUEOUS SOLUTION OF A COMPOUND HAVING THE STRUCTURAL FORMULA